Control device with a control stick, particularly a servo sidestick for aircraft

ABSTRACT

A control device with a control stick, wherein the control stick is moved by an irreversible actuator controlled by a computer, and the computer controls the position of the actuator and thus the movement of the control stick, and slaves the control column position to the force applied, in accordance with force data, from a force sensor, and position data, from a position sensor, through use of a position vs. force law entered in the computer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to control devices having a control stick whichmoves with at least one degree of freedom, usually by translation alongan axis, or even more commonly by pivoting about an axis of rotation.This displacement can be combined with other displacements along otheraxes, actuating other controls. It will be understood that the controlstick may be an aircraft control stick, but may also be a manipulatorfor driving various vehicles, or a control lever for a machine or agame.

2. Description of the Prior Art

Generally speaking, electrical control has been substituted for themechanical control performed by control sticks, and this has enabledmini-joysticks to be created by eliminating any mechanical transmissiondirectly associated with the joystick.

Since the control is electrical, the mechanical reaction of the controlmechanism and of the controlled members (for example, the rudder andailerons of an aeroplane) is no longer felt by the user through thejoystick. It has become apparent that it is worth reproducing anartificial feeling of mechanical reaction in the joystick.

Various mechanical return devices have been proposed, for example usingsprings. U.S. Pat. No. 5,059,882 to Marcillat et at. discloses a devicein which the displacement of the joystick determines a reaction force bymeans of an electromechanical actuator controlled according to apredetermined force vs. position law.

SUMMARY OF THE INVENTION

The object of the invention is to provide a new control device which isapplicable to control sticks in which control is effected by means ofthe displacement of the stick with at least one degree of freedom (suchas pivoting or translation). In the present invention:

the displacement (pivoting or translation) of the stick is produced byan irreversible actuator controlled by a computer;

a force detector is provided both for measuring a force applied by auser to the stick, and for supplying force data to the computer;

a position detector supplies to the computer a feedback of datarepresenting the actual position of the stick; and

the computer controls the operation of the actuator (and therefore thedisplacement of the stick) and servos the position of the actuator andof the stick as a function of the force and position data by means of aposition vs. force law entered in the computer.

Since the actuator is irreversible, it resists movement of the stick dueto the force applied by the user. The measurement of this force istransformed by the force detector into a suitable signal and isconverted by the computer according to the predefined position vs. forcelaw of the stick. This enables the actuator to be controlled so as todisplace the stick to a position which will correspond to the forceapplied.

It is clear that the successive stages into which the operation is splitin fact occur in quick succession. Thus, the user has the impressionthat the stick is moving with the force, and reacting with a reactionforce, similarly to a visco-elastic system.

As used herein, "position detector" refers to means for supplying datawhich is representative of the position of the stick. The positiondetector need not necessarily be a specific component; in particular, itcan be integrated into the drive mechanism before the stick.

The above-referenced position detector, or another independent detector,can be used to output a control signal.

The measurement of the force applied to the stick can also be used tocontrol the steering of the vehicle or the machine. In this way, even ifthe actuator were unable to operate for any reason, and the stick stayedjammed in some position, steering would still be possible by simplyvarying the force applied to the stick.

It will be understood that the invention can be applied to servo controlof movement in two axes of rotation, or in more than one axis oftranslation, and not just a single one. The axes can be de-coupled andindependent, and the servo feedbacks can be different.

Preferably the measurement of the force applied to the stick is made bymeasurement of deformation or displacement of a deformable elasticdevice which is interposed between the stick and the actuator. Theelastic device can be a leaf spring. For example, the leaf spring may befixed to the stick at one end and may be connected to the actuator atthe other end through a hinged joint.

The measurement of the force by means of the deformation of the leafspring enables bigger displacements (of the order of 10⁻² to 1 mm) to besensed than those measured by other systems of force detectors, such asstrain gauges (microscopic movements of the order of 10⁻⁵ to 10⁻³ mm).The corresponding movements of the joystick remain sufficiently small(less than 1 degree) so as not to spoil the physiological impressionthat the user has at the grip.

This means that measurement of the displacements can be made by usinglinear or rotary, inductive or resistive detectors whose reliability,accuracy and stability as a function of time, of temperature andenvironmental conditions are much better than for detectors of theextensometer or piezo-electric kinds. Operating safety is thereforeconsiderably improved.

The principle of measurement of the force applied to a control stick isknown per se, of course, for example from U.S. Pat. No. 4,607,202 toKoenig. However in that case the control stick is mechanical and notelectrical, and the measurement of force is intended to compensate forthe influence introduced by acceleration acting on inertial masses, andnot to provide a servo control of the position of the stick by means ofan irreversible actuator.

The detector is disposed rigidly fixed to the actuator or to the stickitself. For example, the detector can be located on an extension whichis parallel to the leaf spring. The feedback of the position ispreferably arranged in such a way as not to be influenced by the elasticdeformation of the force detector.

The irreversible electromechanical actuator may be a linear screw jack,whose body and plunger are hinged respectively to the chassis of thedevice and to the stick.

The position of the stick can be controlled by the computer by means ofthe stick position detector, for example, placed in parallel on theactuator or integrated into the actuator.

It will be understood that it is possible to provide redundantmeasurement and calculation systems in order to improve safety further.

Moreover, means may advantageously be introduced for varying theposition vs. force law in the parameters of the computer, so as toenable the law to be adapted to the ergonomics of the control, as wellas to enable its real time modification as a function of theconfiguration of the systems controlled.

Other features and advantages of the invention will appear from thefollowing description of an embodiment thereof, which is an example ofthe case where a control system has a single rotational axis.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to the single figure of the accompanying drawingswhich is a diagrammatic view of the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The mini joystick 1 pivots in a plane about a transverse axis ofrotation 2 on a pivot 3 which is indicated merely diagrammatically inthe drawing. It will be understood that the case of rotation about asingle axis is considered herein with the provision of a servo controlfor this movement; the mini joystick 1 may also pivot about a secondaxis orthogonal to the axis 2 by means of a second pivot (not shown),which may be interposed between the mini joystick 1 and the pivot 3, forexample.

A first extension consisting of a leaf spring 4, and a second, rigid,extension 5 are secured to the mini joystick 1 to follow its mainpivoting movement and preferably extend orthogonally to the axis ofrotation. The second extension 5 extends parallel to the first extension4 and provides support for a displacement detector 6. The displacementdetector can be, for example, a sensor acting with or without contact,enabling the relative displacement between the leaf spring 4 and therigid extension 5 to be measured.

The end of the leaf spring 4 is connected to the end of the plunger 9 ofa linear screw jack 10 by means of a hinge 7 which enables it to pivotabout an axis 8 which is parallel to the axis of rotation 2.

The body of the jack 10 is itself hinged about an axis of rotation 12parallel to the axis of rotation 2 at its rear end 11, fixed relative tothe chassis. The chassis, not separately numbered, is indicateddiagrammatically by the well-known symbols for built-in fixity adjacentthe pivot points.

The plunger 9 slides in the body of the jack 10 and is driven by meansof the cooperation of screw threads 13 and 14 and of gear wheels 15 and16. Gear wheels 15 and 16 are drivingly connected to a motor 17.

The motor 17 is controlled by a digital or analogue computer 18.

A position detector 19 is mounted in parallel between the hinges 7 and11 of the jack, and may of course be integrated with the jack 10. Theposition detector measures the effective absolute position of the end ofthe leaf spring 4, which is representative of the effective absoluteposition of the grip 1 relative to the chassis. Noise scatter is,however, eliminated from the measurement, since in this arrangement thedetector responds to the end of the leaf spring and not directly to thegrip. Both the position detector 19 and the displacement detector 6output position data to the computer 18, whose function is to derive thedisplacement commands.

The operation of the device is as follows.

The user applies a force to the grip 1.

On account of the irreversibility of the jack 10, the end of the leafspring 4 resists this force, which therefore causes a (small)deformation of the elastic device which is formed by the leaf spring 4.This deformation is measured by the displacement detector 6 andtransmitted to the computer 18 which interprets it in terms of force.

The computer 18 derives and feeds back a position command which istransmitted to the motor 17. The command is dependent on the positionvs. force law which is entered into the computer.

The jack 10 therefore produces a displacement of the plunger 9 inaccordance with this law and with the dynamic parameters stored in thecomputer memory: accelerations, viscosity, dry friction, thresholds,etc.

The position detector 19 completes the feedback loop for the position ofthe plunger 9 through the computer 18 and the position vs. force law.

This displacement does not cause any change in the deformation of theleaf spring 4, nor the rigid extension 5, Since this deformation onlydepends on the force applied by the user, which only varies at theuser's initiative.

Any modification of the force applied by the user or of the position vs.force law results instantaneously in movement of grip 1.

We claim:
 1. A control device comprising:(a) a control stick which isdisplaceable in at least one degree of freedom and which has auser-applied force applied thereto by a user; (b) means for reproducing,at said control stick, a feeling of a reacting force which reactsagainst the user-applied force; (c) a computer; (d) an irreversibleactuator which is coupled to said control stick and which controlsdisplacement of said control stick, said irreversible actuator in turnbeing coupled to said computer, said control stick being displaceable bysaid irreversible actuator but said irreversible actuator not beingdisplaceable by the user applied force applied to said control stick;(e) a force detector which is associated with said control stick andwhich measures the user-applied force and supplies user-applied forcedata, indicative of the user-applied force, to said computer; and (f) aposition detector which is associated with said control stick and whichsupplies said computer with a feedback of actual position of saidcontrol stick; wherein:said computer controls operation of saidirreversible actuator and thus the displacement of said stick; and saidcomputer servos the position of said control stick to the user-appliedforce, as a function of the user-applied force data and the actualposition of said control stick, via a position versus force law enteredin said computer.
 2. The device of claim 1, wherein said force detectorcomprises a deformable elastic device inserted between said controlstick and said irreversible actuator, deformation of said elastic devicebeing measured as representative of the user-applied force.
 3. Thedevice of claim 2, wherein said elastic device is a leaf spring securedfor movement with said control stick, said leaf spring having a free endconnected to said irreversible actuator by a hinged joint.
 4. The deviceof claim 3, further comprising a displacement detector which detectsdeformation of said leaf spring and which is rigidly fixed for movementwith one of said control stick and said irreversible actuator.
 5. Thedevice of claim 1, wherein said irreversible actuator is a screw jack.6. The device of claim 5, wherein said screw jack comprises a body and aplunger and wherein said device further comprises a chassis, said bodyof said screw jack being hinged on said chassis about a first axis ofrotation, said plunger of said screw jack being hinged on said stickabout a second axis of rotation parallel to said first axis of rotation.7. The device of claim 1, wherein said position detector is used tooutput a control signal.
 8. The device of claim 7, wherein said positiondetector is disposed in parallel with said irreversible actuator.
 9. Thedevice of claim 1, wherein said control stick is displaceable in said atleast one degree of freedom in a pivoting movement.
 10. The device ofclaim 1, wherein measurement of said user-applied force is employed as acontrol signal via said position versus force law, with said controlstick immobilized in any given position.